1. Field of the Invention
This invention generally relates to thermal management of electronic components and more specifically to thermal management of components within a hard disk drive.
2. Description of the Related Art
In a typical hard drive configuration, a preamplifier is mounted on a flexible (flex) cable, connecting the hard disk drive head circuits with the preamplifier, which performs initial amplification of the signals received from the hard disk drive heads. Existing methods for connecting (mounting) preamplifier (preamp) chips on the flex cables of hard disk drives suffer from the lack of good heat conduction of the heat generated by the preamp to the E-block of the drive or convection path to the ambient air flow. As a result, an overheating condition may occur, resulting in a failure of the preamp and the entire hard drive, or a reduction in data throughput performance.
FIG. 1 depicts a general view of a typical preamp flex cable 100 of a hard disk drive. A preamp 101 is mounted onto the flex cable 100, and an underfill 102 is injected below and around the preamp 101, as shown in FIG. 1. The flex cable 100 also includes head circuit mounting areas 103, on which the head circuits of the hard disk drive connect electrically by solder flow, ultrasonic bonding, or other suitable means. The underfill 102 is typically made of a material having both sufficient stiffness to protect the underside BGA solder bumps, and reasonable heat conducting properties, and serves to facilitate the transmission of the heat generated by the preamp to the body of the flex cable.
FIG. 2 is a close-up cross-section view of the preamp 201 and the underfill layer 202. This figure also shows various layers that constitute the flex cable 200. Specifically, the flex cable 200 incorporates an aluminum stiffener 230, which provides mechanical support for the various flex cable layers and the electrical components mounted thereon and an interconnecting traces 250 for facilitating electrical connections between the preamp 201 and various other electrical components attached to the flex cable 200. A circuit fabrication process employing the subtractive method of patterning the interconnecting traces 250 is common for this application. The interconnecting traces 250 are insulated from the stiffener 230 using insulating base layer 220, which can be implemented using polyimide or kapton materials. A base adhesive layer 215 laminates together the base layer 220 with the interconnecting traces 250. Another insulating (polyimide or kapton) cover layer 240 is disposed on top of the copper interconnecting traces 250 and serves to insulate the electrical connections of the flex cable 201 from other components of the hard disk drive. A cover adhesive layer 235 laminates together the base adhesive layer 215 with cover layer 240, atop the interconnecting traces 250. Stiffener adhesive layer 225 attaches stiffener 230 to the circuit base layer 220.
As can be seen from FIG. 2, during the operation of the hard disk drive, to reach the aluminum stiffener 230, the heat generated by the preamp 201 has to travel through the insulating polyimide or kapton layer 220 and base adhesive layer 215. The chief problem with the conventional flex cables is that the polyimide or kapton material of the insulating layer 220 has very poor thermal conductivity properties (about 0.15 W/m-C), which results in poor heat flow between the preamp 201 and the aluminum stiffener 230, which, in turn, may cause the overheating of the preamp 201.
FIG. 3 depicts generally the same view of the flex cable 300 as FIG. 2, except that the underfill 302 is not shown. The removal of the underfill 302 exposes the contact pads 310 that make the electrical contact to the preamp. The contact pads 310 are patterned within the copper interconnecting traces 350 that are laid over the base layer 320, which is made of an insulating material, such as polyimide or kapton. As can be understood from FIG. 3, because of the presence of the thermo-insulating layer 320 underneath the preamp 301, the only path for heat conduction from the preamp is either to the ambient air, which is very low, or via the contact pads laterally outward. Interconnecting traces 350 are small in cross-section and are able to conduct only a slight amount of heat, which unfortunately still stays isolated from the stiffener as a heat sink. Also, since heat can be conducted only via the contact pads, it increases the stress load on the contact pads and may lead to their premature failure.
FIG. 4 depicts the same flex cable, but with the preamp removed for clarity. In accordance with the configuration shown in FIG. 4, the top insulating cover layer of the flex cable is marked with numeral 440. Below this layer, there is the cover adhesive 435 and conductive traces 450, which form the contact pads. Solder bumps 455 are provided, via assembly level solder flow, on the contact pads 410 to facilitate both the electrical and mechanical connections. The conductive traces 450 overlay a base adhesive 415 and insulating base layer 420, which is adhered to a stiffener 430 via stiffener adhesive layer 425.
As stated above, the conventional flex cable configuration shown in FIGS. 1 through 4 suffers from poor heat transfer away from the preamp, which may result in its overheating and failure. Thus, new, more efficient flex cable configuration is necessary.